This application claims the Paris convention priority of Japanese patent application Hei. 10-2613489 filed on Sep. 16, 1998, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of cutting a plate glass member as a mother material of a material to be pressed for use in a reheat press,method, and to a plate glass mother material cutting device, particularly to a method of cutting a plate glass mother material in which a plurality of grooves are scribed/processed beforehand on one main surface, and to a plate glass mother material cutting device.
2. Description of the Related Art
When optical elements such as an optical lens and a prism are formed, press molding is used. Examples of a press molding method mainly include a precision press molding method, a direct press method, and a reheat press method.
The precision press molding method is a molding method of transferring the shape and surface precision of a molding die to a softened glass, and the pressed material requires no grinding or polishing.
On the other hand, the direct press method, and the reheat press method are molding methods based on the premise that after the press molding the grinding for bringing the shape of the pressed material close to a final product shape, and the polishing for polishing the surface of the pressed material are performed.
Since the precision press molding method is free of the polishing, it is suitable for manufacturing lenses having shapes difficult to polish, such as a non-spherical lens. However, in order to reproduce the shape precision of the molding die, pressing has to be performed when the viscosity during pressing is in a relatively high range of 108 to 1012 dPaxc2x7S, and only the glass material satisfying the condition that it fails to be devitrified at the pressing viscosity can be used. Moreover, problems are that a manufacture device is large-scaled and expensive, and that manufacture cost is raised.
Therefore, in order to manufacture a large amount of glass products while the production cost is suppressed, the direct press method and the reheat press method are suitable.
The direct press method comprises injecting a predetermined amount of molten glass flowing out of a discharge pipe into lower and upper dies of the molding die, and performing pressing at a relatively low viscosity of around 103 dPaxc2x7S. According to this method, the pressed material has a good weight precision, but the method is not suitable for the production of a small amount of a wide variety of products.
On the other hand, the reheat press method comprises preparing a material to be pressed having a predetermined weight, reheating the material to be pressed from a normal temperature, softening the material, and performing press molding by the molding die at the viscosity of around 105 dPaxc2x7S. This method is not suitable for the production of a large amount of a small variety of products, but is suitable for the production of the small amount of the wide variety of products. In the reheat press method, when the weight of the material to be pressed is insufficient as compared with a cavity in the press molding die, the cavity of the molding die is insufficiently filled with the material to be pressed, which causes an elongation defect. Moreover, when the material to be pressed has an excessive weight, another problem occurs that the material overflows the molding die. Therefore, in the reheat press method, the weight adjustment of the material to be pressed is a big problem.
As a method of forming the material to be pressed for use in the reheat press method, there is proposed the following method. First, a plurality of lattice grooves are scribed/processed beforehand on one main surface of a plate glass mother material as the mother material of the material to be pressed. Subsequently, the plate glass mother material is laid on a cushioning material in such a manner that these grooves face downward, portions opposite to the grooves are pressurized from above by a rod-like indenter, and cracks are allowed to grow by stress concentration generated in the grooves, thereby performing cutting. After all the grooves are completely cut, a large number of materials to be pressed which are uniform in weight are formed.
In the above-described method of pressing the portions opposite to the grooves to perform the cutting, since in the beginning the plate glass mother material is sufficiently large, a large bending stress is applied to each groove in addition to the pressure by the indenter. Therefore, even when the pressing amount is small, sufficient cutting can be performed. However, as the cutting proceeds, the plate glass mother material is separated, so that the bending stress is reduced, and a large pressure becomes necessary. Therefore, an appropriate pressing amount for each groove also changes in accordance with cutting situations. If the pressing amount is inappropriate, a preferable material to be pressed cannot be formed. Specifically, when the pressure is insufficient, the plate glass mother material could not be cracked. On the other hand, when the pressure is excessively applied, defects such as chipping are caused.
The present invention has been developed in consideration of the above-described problems, and an object thereof is to provide a method of cutting a plate glass mother material in which appropriate pressing is constantly performed and more preferable materials to be pressed can be formed, and a plate glass mother material cutting device.
To solve the problem, according to the present invention, there is provided a method of cutting a plate glass mother material in which a plurality of grooves are scribed/processed beforehand on one main surface, comprising: laying the plate glass mother material on a mounting base with the grooves turned inward; pressing portions opposite to the grooves from the outside by a pressing indenter with a pressing amount according to a cutting order of the grooves; performing control to stop the indenter from advancing after the cutting is completed; and cutting the plate glass mother material.
In the method of cutting the plate glass mother material, the plate glass mother material is laid on the mounting base with the grooves facing inward, the portions opposite to the grooves are pressurized from above by the indenter with the pressing amount according to the cutting order of the grooves, the indenter is controlled to stop from advancing after the cutting is completed, and the plate glass mother material is cut.
Therefore, the pressing amount can be prevented from becoming too much or too little, and the cutting defect of the plate glass mother material, the generation of chipping, and the like can be prevented. Therefore, the materials to be pressed uniform in weight can be formed. Moreover, since control is performed to stop the indenter from advancing after the cutting is completed, no further pressing than necessary is performed. Therefore, the cut glass member is prevented from being chipped.